This invention relates to synthetic polymer latexes useful in coating applications wherein the latexes have coalescing agents incorporated therein.
Films made from many synthetic polymer latexes, particularly acrylic and vinyl ester latexes, are known to have excellent physical properties including superior elasticity, resilience, elongation at break, and pigment binding power; and excellent chemical properties, such as resistance to hydrolysis and solvent attack. Because of these properties, latexes of these polymers are used extensively in many interior and exterior coating applications.
Unfortunately, many such latexes having the aforementioned desirable properties are not film forming in many conventional coating applications. In order to overcome this deficiency, it has been a common practice to add a non-volatile organic liquid, such as alkyl phthalate esters and phosphate esters (commonly referred to as plasticizers), to the latex. These plasticizers soften the resin particles thereby promoting their coalescence into a continuous film. However, such plasticizers reduce the freeze-thaw stability of the latex. Moreover, their presence in the films made from the latexes render the films soft and tacky, thereby causing dirt accumulation problems during drying.
In order to overcome these problems, it has become a common practice to add a volatile plasticizer (often referred to as a "transient plasticizer" or fugitive coalescing agent) to the latex. See, for example, The Applications of Synthetic Resin Emulsions by H. Warson, published in 1972 by Ernest Benn Limited, London, Chapter III, "General Polymer Emulsion Application".
However, to be effective, the volatile plasticizer must not cause latex destabilization during its addition to the latex (commonly referred to as shock), must maintain a high coalescence efficiency and must not produce odor during evaporation. It has been found that certain compounds, such as aliphatic glycols, aliphatic glycol ethers (U.S. Pat. No. 3,790,520), aromatic glycol ethers and acetate capped glycol ethers are acceptable as fugitive coalescing agents in most coating applications. Common examples of these include ethylene glycol phenyl ether; 2,2,4-trimethyl 1,3-pentanediolmonoisobutyrate; and diethylene glycol n-butyl ether acetate. Unfortunately these plasticizers evaporate slowly, thus increasing drying times and intervals between recoating.
In view of the aforementioned deficiencies, it remains highly desirable to furnish a latex composition which, when applied as a coating, will dry rapidly to form a non-tacky film having the physical properties characteristic of the latex polymer in virgin form.